How to Treat Reversible Cardiac Arrest Causes Thru ACLS Algorithm

Sudden cardiac arrest occurs without warning or reason. In these cases, it may not be possible to identify an immediate cause of arrest. For example, congenital heart defects may lead to sudden cardiac arrest, and surgery or other invasive treatments may be necessary. However, the most common causes of cardiac arrest, the “Hs and Ts,” which are typically the result of trauma or chronic health problems, can be reversed through proper treatment. The Advanced Cardiac Life Support (ACLS algorithm) includes the treatment of causes of cardiac arrest after performing initial interventions, and completing an advanced course to provide ACLS will increase survival chances.

emergency team carrying a patientWhy Treating Causes of Arrest Is Essential to ROSC

The premise of cardiopulmonary resuscitation (CPR) and ACLS is to encourage a return of spontaneous circulation (ROSC). The name implies the heart restarting with the proper electrical signals and providing blood flow to the body. Unfortunately, left unchecked, reversible causes of arrest will result in a weak or prolonged interval between the time of cardiac arrest and ROSC.

The only solution to ensuring ROSC without returning to cardiac arrest in the minutes following lies in treating the reversible causes. Failure to address the causes will lead to a subsequent arrest, and subsequent arrest increases mortality risk. Thus, preventing subsequent arrest is essential to survival. Recurrence of cardiac arrest also increases the risk of long-term injury, including brain and organ damage.

The ACLS Algorithm Defines When to Treat Reversible Causes of Arrest

A second spent trying to treat a cause of arrest that delays the initiation of chest compressions could result in death. The ACLS algorithm advises the treatment of reversible causes of arrest following the initial, two-minute cycle of chest compressions and a dosage of epinephrine, following an EKG reading of asystole or pulseless electrical activity (PEA).

If the rhythm is a shockable rhythm, the algorithm advises the administration of a shock, followed by CPR and obtaining an IV/IO access. Among those suffering from a shockable rhythm, treating the reversible causes only occurs after completing the second round of CPR and administering epinephrine.

The algorithm notes that the reversible causes of arrest typically result in a non-shockable rhythm. This is why performing CPR takes precedence over treating the reversible causes of arrest within the first two minutes. An exception is when someone enters cardiac arrest following the anaphylactic reaction that leads to the closure of the trachea. In these cases, the immediate administration of epinephrine will reverse the reaction. However, severe reactions may require subsequent dosing and ACLS if the person’s heart stops beating as part of the algorithm. Therefore, the algorithm’s instruction to administer epinephrine is also an intervention to treat a reversible cause of arrest.

Above all else, keep in mind that you must follow the ACLS algorithm until ROSC is achieved or a licensed individual, such as RN, physician, justice of the peace or a paramedic, pronounces death. This includes performing chest compressions, administering electrical shocks, administering proper medications, and performing rescue breaths. Depending on the number of workers involved, it is possible to work on treating the reversible causes of arrest while performing chest compressions or other steps in the algorithm.

The reversible causes of cardiac arrest can be broken down into two categories: those that start with “H” and those that start with “T.”

Causes of Arrest That Start With “H”


Hypoxia is a life-threatening condition that results when the lungs are incapable of functioning correctly and do not provide enough oxygen to maintain perfusion to tissues. The decrease in oxygen perfusion leads to stress and the buildup of lactic acid throughout the body’s muscles. In coronary vessels, this amounts to a loss of oxygen for cardiac muscle, which may lead to tissue death and loss of electrical activity.

Treatment: The treatment for hypoxia depends on the cause. Since it may result from exposure to carbon monoxide (CO), drowning, asphyxiation, lung disorders, or extreme sedation, such as an opioid overdose, the treatment will change. In general, it includes establishing an advanced airway, performing rescue breaths as part of CPR and ACLS, and the administration of oxygen.

A key difference exists for those suffering from CO poisoning. CO binds to hemoglobin at an affinity significantly higher than that of oxygen. The person may get enough oxygen from an advanced airway to achieve ROSC, but immediate treatment in a hyperbaric chamber is necessary. A hyperbaric chamber operates at a higher atmospheric pressure. The increased pressure forces CO molecules to unbind from the hemoglobin. Since the pressure is increased with oxygen, oxygen molecules readily bind to hemoglobin, restoring healthy oxygen perfusion.


Hypovolemia refers to the loss of a significant volume of bodily fluids, typically blood. Traumatic blood loss, gastrointestinal bleed, severe diarrhea and vomiting, ongoing dehydration, or even extreme sweating may result in decreased blood flow and loss of perfusion. As the body enters a state of shock, the heart weakens and eventually stops beating. The simplest way to think about this cause is looking at a hand-held water pump. If enough water is in the pump, it will work just fine. If the water level decreases, the pump has a more difficult time moving water through the tubes. The same principle affects the heart.

Treatment: While proper chest compressions and rescue breaths will help the remaining volume circulate, the root of the problem must be treated. This includes the administration of plasma, IV fluids, blood, and clotting factors, depending on the issue leading to the decreased volume of blood fluids.

For instance, someone with a form of hemophilia and suffering from extreme blood loss may require both the administration of blood products, pressure to the wound and clotting factors to stop the bleeding and increase the volume of blood.

Hydrogen Ion Buildup

Also known as acidosis, a high concentration of hydrogen ions in the blood may lead to cardiac arrest. Any solution with a higher concentration of hydrogen ions has an acidic pH level, and in the body, this may be the result of metabolic or respiratory actions. Drawing an arterial blood gas provides an immediate determination of whether the person is suffering from acidosis.

Treatment: Respiratory acidosis is treated by providing proper ventilation and oxygen. Meanwhile, metabolic acidosis is treated with the administration of sodium bicarbonate.


Potassium is one of the significant electrolytes used by the body to enable muscle contraction and the transmission of electrical signals through nerves, also known as action potentials. If the potassium level becomes extreme in either direction (hypokalemia for too little or hyperkalemia for too much), cardiac arrest is likely. Causes of these conditions may range from chronic kidney disease to consuming too much potassium in the diet. Ultimately, the heart lacks the electrolytes necessary to contract and conduct electrical signals.

Treatment: Treatment for hyper/ hypokalemia depends on which direction the level has moved. Having too little potassium is treatable with an infusion of potassium. Hyperkalemia can be treated with dialysis for those suffering from kidney disease or medications, including sodium bicarbonate or calcium.


Hypothermia is one of the most uncommon causes of arrest and occurs when the body’s core temperature drops significantly. The official threshold is 30 C or 86 F. At this temperature, cardiac output decreases, increasing the risk for cardiac arrest. Unfortunately, CPR and defibrillation have the potential to be ineffective for treating this cause.

Treatment: The immediate solution to hypothermia is rewarming. Although it would seem to indicate rewarming takes precedence over CPR, the specific actions will depend on the capabilities of your facility. If external warming with blankets and heat sources is possible, you may begin CPR provided, it doesn’t interfere with the rewarming process. The unusual approach to hypothermia results from the potential for tissue preservation while in a hypothermic state. Although a cause of cardiac arrest, hypothermia is one of the few conditions where it may be advisable to hold off on CPR until directed to begin CPR during rewarming. However, if you lack such direction, administering ACLS and rewarming the body simultaneously is preferred.

Causes of Arrest Beginning With “T”

Tension Pneumothorax

Meaning “tension caused by air in the thorax,” a tension pneumothorax occurs when  perforation occurs in the protective membranes covering the lungs. The lungs have two such membranes, and when the pressure between the membranes becomes equal to the atmospheric pressure, the lungs cannot function. The lungs function on the basic principles of aerodynamics which create a negative-pressure space through the expansion of their volume. The buildup of pressure equalizes the pressure in the pleural space with that of the atmosphere. As a result, when the person breathes in, the lungs are incapable of drawing oxygen into the body.

Treatment: The best cure for a tension pneumothorax is to remove the air from the pleural space through needle decompression or a chest tube.

Tamponade, Cardiac

Cardiac tamponade occurs when the pericardial sac, which surrounds the heart, fills with fluid or blood. The fluid places additional pressure on the heart, constricting the ventricles’ ability to expand and limiting blood flow, and its typical cause is the perforation of the sac, explains

Treatment: The treatment requires drainage with a needle through a procedure known as pericardiocentesis or surgical options, such as a thoracotomy.


Any substance can reach toxic levels in the blood, but in this discussion, toxins are limited to toxins introduced through animal bites and the ingestion of poisons.

Treatment: With the exception of antidotes for specific, known toxins, such as rattlesnake antivenom, there are not currently any particular recommendations for the treatment of toxicity in the course of ACLS. Therefore, treatment may begin if the toxin is known and susceptible to a given antidote. If the toxin is unknown, it is unreasonable to attempt treatment until a consultation by a toxicologist is performed after ROSC, explains ECCGuidelines.Heart.Org.

Thromboses, Including Pulmonary and Coronary Thrombosis

Thrombosis refers to a blockage of a major vessel. Pulmonary thrombosis, also known as a pulmonary embolism, results when a blockage occurs in the pulmonary artery or vein. As a result, the heart cannot receive adequate blood flow. Coronary thrombosis occurs when a blockage occurs in one of the vessels providing blood flow to cardiac tissue. The result is a myocardial infarction (heart attack).

Treatment:  The treatment for a pulmonary embolism may include fibrinolytic therapy, an embolectomy, or the administration of anticoagulants. The first option is surgical, and the latter are medications that treat the embolus.

Addressing a coronary thrombosis is more complicated. It requires an angioplasty, stent placement, or even coronary bypass surgery. The treatment depends on the severity of the blockage and the likelihood of its recurrence.

infographic causes of arrest beginning with t

Know the Reversible Causes of Arrest and How to Treat Them

Cardiac arrest is a life-threatening emergency. It may occur suddenly and without warning, or it may be the result of specific causes that can be successfully reversed. The urgency of cardiac arrest requires health care professionals to know when to address the reversible causes in the course of administering ACLS and how to treat each one. Failure to treat reversible causes promptly will result in a decreased chance of ROSC and poor outcomes, including death.

Have you ever encountered a cause of arrest that falls outside of the common “Hs and Ts?” Share it along with this article to social media. Through shared experiences and continuous education, we can save more lives. Also, remember to enroll in your advanced care course to treat cardiac arrest too!

About Mackenzie Thompson, Life Saver, NHCPS

Mackenzie is a seasoned life saver and a multifaceted professional in the medical field. With an impressive 8-year track record in medical education, Mackenzie boasts a comprehensive set of certifications, including ACLS, PALS, BLS, and CPR, which reflect her unwavering commitment and expertise. Her significant contributions to teaching and the development of medical content underscore her profound knowledge and dedication to advancing healthcare.

Beyond her medical prowess, Mackenzie seamlessly integrates her passion for education with her proficiency in media and marketing. Her academic journey at Indiana University culminated in a degree in Media and Marketing, further solidifying her expertise in these domains.

In addition to her impressive professional achievements, Mackenzie possesses a refined taste for global exploration, photography, design aesthetics, sartorial elegance, and the culinary arts, with a particular affinity for Chinese cuisine. Currently based in the vibrant city of Manhattan, she continues to be a driving force in the medical community. She is an invaluable asset to, where she champions excellence and innovation with unwavering dedication.

Contact Mackenzie Thompson, Life Saver, NHCPS at.

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